1. Field of Invention
The present invention relates to an electrode of an electrochemical cell, in particularly a fuel cell, and a method of fabricating the same. Moreover, the present invention relates to an electrode having ionic channels constructed with ionomers and a method of fabricating the same.
2. Description of Related Art
Fuel cell technologies have been explored as a viable alternative of energy sources for at least the reasons that they produce less emission than the carbon-based fuels. A fuel cell is a device that converts chemical energy directly into electrical energy. Basically, a fuel cell works by separating electrons and protons of a reactant fuel and forcing the electrons to travel through a circuit to produce electrical power. Hence, a fuel cell has a higher efficiency than the ordinary internal combustion engines by bypassing the intermediate conversions to thermal energy and mechanical energy before the energy is transformed into electricity. There are many types of fuel cell, which are usually classified by the electrolyte employed in the cell or the operating temperature of the fuel cell. For example, there are the Alkaline Fuel Cell (AFC), the Proton Exchange Membrane (PEM) Fuel Cell, the Direct Methanol Fuel Cell (MDFC), the Phosphoric Acid Fuel Cell (PAFC), the Molten Carbonate Fuel Cell (MCFC) and the Solid Oxide Fuel Cell (SOFC).
The basic structure of all fuel cells is similar. The cell typically consists of two electrodes (an anode and a cathode) that are separated by an electrolyte and are connected to an external circuit. The electrodes are exposed to gas (e.g. hydrogen or oxygen) or liquid flows in which reactions occur to create a potential difference across the cell. For example, in a PEM fuel cell, the pressurized hydrogen gas enters through the anode side of the fuel cell. At the catalyst on the anode, the hydrogen molecule splits into two hydrogen ions (H+) and two electrons (e−). The hydrogen ions travel to the cathode through the electrolyte, and the electrons travel through the external circuit. The electrolyte in a PEM fuel cell is a proton exchange membrane which conducts only positively charged ions and blocks electrons. At the cathode, oxygen molecules dissociate and accept the electrons from the external circuit. The hydrogen and oxygen ions then combine to form water.
The main requirement of a good electrode for an electrochemical cell is to provide large three-phase-boundary region among the reactant molecules, the catalyst particles with continuous electronic pathway and the ionic conductor for ensuring both good electronic and ionic conduction and the redox reaction of reactant molecules. The three-phase-boundary region is typically formed by the catalyst particles, the ionomeric binders and the reactants in the porous support structure. Electronic conductivity is provided by the carbon support which the catalyst particles are supported on, while ionic conductivity is provided by the ionomeric binders.
In order to expedite electrochemical reactions for improving the performance of an electrochemical device, in particularly a fuel cell, ionic and electronic conductions must be facilitated. Further, catalysts are usually formed with expensive noble metals, such as platinum, which is one of the major expenses for fuel cells. Hence, it is also important to improve catalytic efficiency.